1. Field of the Invention
The present invention relates to ink jet heads of ink jet printers, and more particularly, to an ink jet head utilizing electroviscous fluid for control of ink discharge.
2. Description of the Background Art
A typical conventional ink jet head forming an image by discharging droplets of recording liquid is called a XEYSER type ink jet head, and is disclosed in U.S. Pat. No. 3,946,398. According to this head, an electric signal is applied to a piezo oscillator attached to a recording head including an orifice to reduce the volume within an ink chamber, whereby pressure is generated to discharge ink. This head must have a plurality of piezo oscillators attached corresponding to each of a plurality of discharge channels. It is difficult to reduce the size of a piezo oscillator. Therefore, this head had a problem that down-sizing is difficult and print out at high density was inhibited.
In order to solve the above problem, Japanese Patent Laying-Open No. 2-172746 discloses a head that utilizes electroviscous fluid for controlling ink discharge. Here, this electroviscous fluid is a liquid having dielectric solid particles and dielectric compounds dispersed within an electrical insulative liquid, and exhibits the Winslow effect in which the viscosity is altered suddenly by having a voltage applied.
FIG. 1 is a schematic diagram of a conventional ink jet head utilizing electroviscous fluid for control of ink discharge. Referring to FIG. 1, an ink jet head includes a main body 529 with a cavity 526 for accommodating recording liquid 527 which is a mixture of ink and electroviscous fluid. Main body 529 includes sidewall pairs of 528A, 528B, . . . , 528E, each forming channel nozzles 522A, 522B, . . . 522E with orifices 521A, 521B, . . . , 521E for discharging droplets 523, a piezo-electric element provided within cavity 526 for generating a pressure wave to recording liquid 527, and control electrode pairs 524A, 524B, . . . 524E provided at respective sides of orifices 521A, 521B, . . . 521E for applying an electric field to recording liquid 527.
The pressure generated within cavity 526 by the deflection deformation of piezo oscillator 525 is conveyed to recording liquid 527 including ink mixed with electroviscous fluid. Recording liquid 527 arrives at each of channel nozzles 522A-522E to be discharged from orifices 521A-521E as droplets 523. Control electrodes 524A-524E in the proximity of the orifices apply a voltage to recording liquid 527 in a non-recording channel, whereby the viscosity of ink in the proximity of the orifice is increased to prevent discharge.
According to this technique, the recording head can be formed of a plurality of piezo oscillators fewer in number than the ink discharge channels. Therefore, reduction in size of the recording head and print out at high density can be realized.
However, this technique has the following problems since the electroviscous fluid per se is used as the recording liquid. In other words, the electroviscous fluid is mixed with ink and consumed. Therefore, the characteristics as electroviscous fluid and the characteristics as ink both must be achieved. It is for this reason that the characteristics as ink becomes unstable. As a result, clogging occurs to prevent printing of a favorable quality. Degradation in the dispersibility of the colorant causes generation of precipitation and clogging. Also, the colorant adheres to the electrode by application of a voltage to the recording liquid. Furthermore, the running cost of the recording liquid is high since the electroviscous fluid is consumed together with the ink.